Method and apparatus for recognizing 3-D objects

ABSTRACT

A method and apparatus for recognizing an object, comprising providing a set of scene features from a scene, pruning a set of model features, generating a set of hypotheses associated with the pruned set of model features for the set of scene features, pruning the set of hypotheses, and verifying the set of pruned hypotheses is provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional patent applicationSer. No. 60/581,793, filed Jun. 22, 2004, the entire disclosure of whichis herein incorporated by reference.

GOVERNMENT RIGHTS IN THIS INVENTION

The present invention was made with U.S. government support undercontract number F33615-02-C-1264 (DARPA). The U.S. government hascertain rights in the present invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to 3-D objectrecognition and, in particular, to a method and apparatus for 3-D objectrecognition using indexing and verification methods.

2. Description of the Related Art

Object recognition, such as 3-D object recognition, involves thesolution of several complicated problems. For example, there is (1) theunknown pose between the scene feature (e.g., several related points ofa scene object in 3-D space) and the model, (2) the scene feature-modeldiscrepancy due to occlusions and clutter in a given scene, and (3) thecomputational cost of comparing each individual model from a modeldatabase to match against the inputted scene feature. Alignment-basedverification techniques have been used to address the first twoproblems. However, existing alignment-based techniques apply sequentialRANSAC-based techniques to each individual model from the database andhence, do not address the computational issues related to the thirdproblem when mapping to a large model database.

Stated another way, where there is a large model database and aninputted scene feature having several points, a determination must bemade as to which model corresponds to this scene feature or set of scenefeatures. Because of the limitation of sensors, the scene feature can benoisy and particularly occluded as compared with the model database.Therefore, indexing of the scene feature obtained from the scene for 3-Drecognition and matching the model must be performed very quickly. Forexample, there may be between about 100 to 200 models in a givendatabase. Each model has several hundred model features associatedtherewith. Traditionally, there has to be a comparison of the scenefeatures with the model features in the model database sequentially(e.g., one-by-one). This is very time consuming, computationallyextensive and costly.

Geometric hashing and its variants perform object recognition using highdimensional representations that combine (quasi-)invariant coordinaterepresentations with geometric coordinate hashing to prune a modeldatabase while employing geometric constraints. However, the time andspace complexity of creating geometric cache tables is polynomial in thenumber of feature points associated with each model. Furthermore,because the (quasi-)invariant coordinate representations are relativelylow-dimensional (e.g., typically two or three), the hash table canbecome crowded even with small model databases and the runtimecomplexity can deteriorate to a linear complexity that again does notscale with the size of the database.

Thus, there is a need in the art for a joint feature-based modelindexing and geometric constraint based alignment pipeline for efficientand accurate recognition of objects and especially 3-D objects.Furthermore, there is a need for recognition techniques used inrecognizing 3-D objects from a large model database of 3-D range images.

SUMMARY OF THE INVENTION

Embodiments of the present invention are directed to generating posehypotheses for transforming scene features with high probability ofbeing a match against one or more model features and scoring those modelfeatures with robust match or verification measures. In one embodiment,by employing approximate high dimensional nearest-neighbor searchtechniques, embodiments of the present invention avoid or at leastsubstantially minimize the problem of premature model pruning whilemaintaining the accuracy of alignment-based verification methods.

In accordance with one embodiment of the present invention, there isprovided a method for recognizing an object, comprising providing a setof scene features from a scene, pruning a set of model features,generating a set of hypotheses associated with said pruned set of modelfeatures for said set of scene features, pruning said set of hypotheses,and verifying said set of pruned hypotheses.

BRIEF DESCRIPTION OF THE DRAWINGS

So the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe present invention, briefly summarized above, may be had by referenceto embodiments, some of which are illustrated in the appended drawings.It is to be noted; however, the appended drawings illustrate onlytypical embodiments of this present invention and are therefore not tobe considered limiting of its scope, for the present invention may admitto other equally effective embodiments.

FIG. 1 is a flow diagram of a method in accordance with an embodiment ofthe present invention;

FIG. 2 is an illustration of the method of FIG. 1; and

FIG. 3 is a block diagram of an image processing apparatus forimplementing the above-mentioned methods in accordance with a furtherembodiment of the present invention.

DETAILED DESCRIPTION

In accordance with embodiments of the present invention, there isprovided certain methods that relate to appearance feature andalignment-based approaches to object recognition. In certainembodiments, for example, regarding 3-D models and range images, and 3-Dpoint clouds, “appearance” and features are computed not based onintensities or color but on semi-local 3-D configuration of points inthe scenes and models. Under a feature-based framework, both the modeland the scene objects are represented as a collection of shape features,or signatures, or scene features. By way of example, but in no waylimiting the scope of the present invention, one example of scenefeatures are 3-D shape descriptor images. Furthermore, one example ofscene features may comprise spin images.

The scene features represent appearance as a high-dimensional featureand have an associated local coordinate system, a 3-D location on theobject and a local normal. Therefore, each feature encapsulates thelocal distribution of 3-D points within its scope and also is in acoordinate geometric relation with other features on the scene object.Recognition methods typically vary according to their treatments of thescene feature attributes in the feature configurations.

Embodiments of the present invention are improvements over variants ofgeometric hashing that employ higher dimensional feature. Random SampleConsensus (RANSAC) is an effective data-driven alignment andverification technique. Instead of generating pose hypothesesexhaustively, RANSAC generates only a limited number of hypotheses witha sampling process guided by the matching of scene and model featureattributes.

Generation of potentially good quality pose hypotheses can be aided bythe use of high-dimensional appearance features by employing approximate“nearest neighbor” search methods. One example of a nearest neighborsearch method is called Locality-Sensitive Hashing (LSH). LSH is a formof indexing or a probabilistic method for approximating nearest neighborsearch and achieving sub linear complexity in the number of features ina database. Embodiments of the present invention include methods thatuse both high-dimensional feature attributes and global geometricconfigurations for recognition.

For purposes of the present invention, the following notations should beconsidered:

For the scene object, a set of scene features {b₁, b₂, . . . , b_(s)}and a set of normals to the surface {q₁, q₂, . . . , q_(s)} are computedat basis points {p₁, p₂, . . . , p_(s)) uniformly sampled along thesurface of the object, where b_(k) ε R^(d), p_(k), q_(k) ε R³, d is thenumber of bins in each scene feature or spin image, and s is the numberof scene features or spin images in the scene object. Let α^(k)=(b_(k),p_(k), q_(k)), k=1, . . . , s, representing an augmented spin image thatincludes its local coordinate system, and q be the set of all augmentedspin images.

Similarly, let β^(k) _(i)=(b^(k) _(i), p^(k) _(i), q^(k) _(i), i), k=1,. . . , t_(i) be an entry in the model database, where t_(i) is thenumber of scene features or spin images in the ith model. In oneembodiment, the parameter i can be implemented as a model ID, e.g., amodel identifier. Embodiments of the present invention will generallyrefer to α and β as scene features and model features, respectively, inthe following discussion.

In addition, b_(k) is equal to a 3-D surface descriptor; p_(k) is equalto the basis point (location); and q_(k) is equal to the normaldirection of the plane at the location p_(k). α^(k) equals a scenefeature. β^(k) _(i) equals a model feature. And i equals a model ID oridentity in the feature (e.g., hash model ID in to the feature).

As mentioned previously, solving the likelihood among pose hypotheses ina models database with pose hypotheses generated to transform allpossible pairs of scene features to model features is prohibitivelyexpensive. On the other hand, it is also important to insure theaccuracy if only a small portion of these hypotheses are used.

Embodiments of the present invention use three steps, e.g., scenefeature (e.g., spin image-based) pruning, doublet-based pruning, andRANSAC-based verification, to mitigate these problems. Spin image-basedfeature pruning or scene feature pruning uses one scene feature at atime to prune the model features whose scene features are not similar inthe parameter space. With the assistance of LSH, this step is processedvery efficiently without sequentially accessing all of the modelfeatures in the models database.

Doublet-based pruning (discussed further herein below) uses a pair ofscene features at a time to prune the model-pose hypotheses that areinconsistent with the double constraint. The doublet constraint is apowerful constraint that, in one embodiment, uses both distance andsurface normal to check the consistency between the scene feature pairand the model feature pair. After the first two steps, the remainingpose hypotheses are verified by warping or transforming all the featuresof the hypothesized model to the scene features with the hypothesizedposes. After warping or transforming the likelihood of the hypothesizedmodel being matched with the scene feature, a score is computed based onthe consensus features. The maximum likelihood is recorded for the eachhypothesized model, and the model with the highest maximum likelihood isselected as the match out of all the pose hypothesized models.

Turning now to FIG. 1, there is provided a flow diagram depicting amethod 100 in accordance with an embodiment of the present invention.The method 100 is for recognizing, in one embodiment, a 3-D object andbegins at step 102. The present invention contemplates other objectrecognition methods and techniques not limited to 3-D objectrecognition. For purposes of clarity, embodiments of the presentinvention are described with respect to 3-D object recognition.

The method proceeds to step 104 where a set of scene features isprovided for inputting into the models database for comparison withstored model features. For example, the set of scene features isobtained from an input or query scene, e.g., of a vehicle with aparticular pose. At step 105, a set of model features are first prunedout of the models database using, for example, the LSH techniquedescribed herein. At step 106, a set of pose hypotheses are generatedbased on the likely matching of the scene features inputted from thequery or input scene object with model features. This scene object maybe slightly occluded in an embodiment and the method can still becapable of substantially recognizing the inputted scene object. At step108, the set of pose hypotheses are pruned. At step 110, a verificationmethod is applied to the pruned set of pose hypotheses. At step 112, themethod ends.

Regarding step 106, e.g., the generation of a set of hypotheses, thisstep may comprise transforming at least one scene feature into at leastone model feature. It also may comprise transforming a plurality ofscene features into a plurality of model features. The step 108 ofpruning the set of pose hypotheses may comprise at least two sub stepsof pruning. For example, the step of pruning the set of hypotheses ofmodel features may first include applying surface descriptor parametersto remove bogus model features and thus limit the amount of modelfeatures available for the next step. This may be on the order of about10,000 to 20,000 model features. The numerical data discussed above isonly for illustrative purposes and is not intended to limit the scope ofthe present invention in any way.

In the next sub step of pruning under step 108, in one embodiment of thepresent invention, there may be an application of a doublet-basedhypothesis generation and pruning to remove bogus model features. Theapplying of doublet-based pruning may comprise obtaining a matched pairof scene features with a pair of model features. From this set ofmatched pairs, at least one pose hypothesis may be generated.

The step of obtaining a pair of scene features and corresponding pair ofmodel features may comprise, in one embodiment, associating angle to anormal and distance between each feature in each set of pairs todetermine whether or not a match has occurred. If the compared set ofscene features and model features have substantially the same distancebetween the two objects in each pair and the same or substantially thesame angle from normal between the objects in each pair, for example,then there is a likely match and the pose hypotheses of that model iskept. For all other pairs, where the distance and angle do not match orare not substantially the same, those pose hypotheses are pruned away.

Returning now to the surface descriptor-based feature pruning with LSH,the following is the description of one form of pruning with LSH. Givena single high-dimensional space is extremely time consuming. LSH is aprobabilistic solution for the approximate nearest neighbor problem.

The unique property of LSH is that it relates the probability ofcollision to the L₁ distance between two vectors. In other words, in oneembodiment, if two vectors are close in distance, they will have highprobability of landing in the same bucket of the hash table. The problemof finding the nearest neighbors then turns to then searching only thevectors in the bucket that have the same hash code as the scene featurevector.

The probability of collision as the function of the L₁ distance has thefollowing form: P_(c)=1−(1−(1−d/d_(c))^(K))^(L), where d_(c) is aconstant related to the maximum distance between any two vectors in theset under the consideration, d is the actual distance between twovectors, K is the number of bits used to sample the vectors in theHamming space, and L is the number of hash tables.

Returning now to the doublet-based hypothesis generation and pruningstep, there is provided an embodiment of the present invention asfollows. From a pair of scene features (α^(l) ¹ , α^(l) ² ) and acorresponding pair of model features (β^(k) ¹ _(i), β^(k) ² _(i)), onecan generate a pose hypotheses Φ_(i) for the ith model. A goodhypothesis should be geometrically consistent, that is, if one warps(β^(k) ¹ _(i), β^(k) ² _(i)) to (α^(l) ¹ , α^(l) ² ) according to thehypothesized pose, both the locations and the normal directions shouldbe substantially similar between the corresponding features.

Because an actual pose computation may involve SVD decomposition of a3×3 matrix and some other expensive operations, one would use a cascadedfilter using the four doublet geometric constraints. Given a pair ofcorrespondences, one can apply these four constraints sequentially andcompute the real pose only if it passes all of them. In this way, onecan throw away bogus hypotheses early on without spending time computingan actual pose. In order to compute stable pose from correspondingscene-model pairs that pass the consistency check, one would alsorequire that ∥p^(l) ¹ −p^(l) ² ∥≧d_(min), and arccos(q^(l) ¹ ^(T) ·q^(l)² )≧θ_(min).

Regarding step 110 relating to the verification method application, thisis referred to herein as a likelihood computation. That is, once a posehypotheses θ_(i) is generated for a hypothesized model i, one can warpor transform all the features of the model into the scene coordinatesystem. For each scene feature α^(l), one can then search for a warpedmodel feature B ¹ _(i) that maximizes the likelihood. The followingformulae will be discussed immediately following.

Once a pose hypothesis Φ_(i) ^(·) generated for the hypothesized modeli, in one embodiment, the system can warp all the features of the modelinto the query coordinate system. For each query feature α^(l), themethod then searches for a warped model feature B^(k) ¹ _(i) thatmaximizes the likelihoodp(α^(l),β_(i) ^(k)|Φ_(i) ^(·))=p _(o)(α^(l),β_(i) ^(k)|Φ_(i)) p_(n)(α^(l),β_(i) ^(k)|Φ_(i) ^(·)) p _(s)(α^(l),β_(i) ^(k)),   (1),where p_(s)(α^(l),β_(i) ^(k)) measures the similarity between the spinimages b^(I) and b_(i) ^(k), p_(o)(α^(l),β_(i) ^(k)|Φ_(i)) is theprobability of matching the origins given the pose $\begin{matrix}{p_{o} \propto \left\{ \begin{matrix}{{\exp\left\lbrack {- \frac{\left( {p^{l} - p_{i}^{k}} \right)^{2}}{2_{\sigma}^{2}}} \right\rbrack},{{{if}\quad{{p^{l} - p_{i}^{k}}}} \leq \Delta}} \\{{\exp\left( {- \frac{\Delta^{2}}{2_{\sigma}^{2}}} \right)},{{if}\quad\Delta\left\langle {{{{p^{l} - p_{i}^{k}}} \leq \Delta_{\max}},} \right.}} \\{0,{otherwise}}\end{matrix} \right.} & (2)\end{matrix}$and p_(n)(α^(l),β_(i) ^(k)|Φ_(i) ^(·)) is the probability of matchingthe normals given the posep_(n)=}(q_(i) ^(k) ^(T) ·q^(l))≦η_(max)   (3)

In formula (2), Δ is a threshold suitably chosen to separate inliersfrom outliers, Δ_(max) is the maximum spread of the outliers. We haveassumed that the distribution of the inliers is Gaussian, and havingnoise standard deviation σ. In formula (3), η_(max) is the maximum angleerror.

The likelihood of the pose given the query can then be computed assumingthat the query features are independent $\begin{matrix}{{p\left( {Q❘\Phi_{i}^{\cdot}} \right)} = {\prod\limits_{l = 1}^{s}{{p\left( {\alpha^{l},{\beta_{i}^{k_{l}}❘\Phi_{i}^{\cdot}}} \right)}.}}} & (4)\end{matrix}$Note in formula (4) that β_(i) ^(k) ^(l) is the warped model featurethat maximizes the likelihood in formula (1). The query feature α^(l) isinlier if pα^(l),β_(i) ^(k) ^(l) |Φ_(i) ^(·)) is large.

The likelihood calculation of the aforementioned formulae (e.g.,formulae (1) to (4)) associates a measure of how well a pose hypothesisbelonging to model k (recall generated by a doublet that passes certainconstraints) will fit a model. For each query, one has calculatedsurface descriptors (α), which consist of the location and normal of thesurface where the surface descriptor was estimated together with thesignature (e.g., spin image), which quantifies the local surfaceinformation in the neighborhood of the surface feature α.

Given the features β similarly pre-computed for the model k, one needsto associate each α_(i) feature in the scene feature to one of the βfeatures from the model k. That is, the feature β_(j), which has thebest match to α_(i). (See formula (1).) Formula (1) states that oneassigns a scene feature to the model feature (of course after the modelfeature has been warped towards the scene), which yields the best match(e.g., the highest probability of correspondence).

Formulas (2) and (3) provide a means of computing the individualprobability of correspondence. One also takes into account outliers inorder to have a robust matching score. That is the role of thresholdsΔ_(max) in formula (2) and η_(max) at formula (3). If the error islarger than these thresholds, the user limits the error associated tothat match such that a single bogus correspondence will not overwhelmthe final score. Formula (4) expresses that each individual probabilityof matching is combined in a final score by assuming that each match isindependent.

Turning now to FIG. 2, which is an illustration of the method 200described herein above. The cones and dashed lines represent possiblematches. Solid lines represent solved matches. In FIG. 2, section (a), ascene object or input scene 202 is provided. Initially, any one of thescene features 204 can be matched with any one of the model features 206as represented by a cone 208. Here, at least three models 210 ₁, 210 ₂and 210 ₃ have been selected. In FIG. 2, section (b), after scenefeature-based pruning, there are fewer possible matches 212 remainingfor the left most vehicle 210 ₁ because other the vehicles' modelfeatures 210 ₂, ₃ are more similar to the set of scene feature 204. As aresult, only a few pose hypotheses will be generated for this model.This stage involves only one scene feature at a time.

In FIG. 2, section (c), after doublet-based pruning, possible matches212 between the scene features 204 and the possible models 210 aredramatically reduced. The left most vehicle 210 ₁ does not have anypossible matches and is no longer considered for matching beyond thispoint. This stage involves a pair of scene features at a time.

In FIG. 2, section (d), after RANSAC based verification, the right model210 ₃ is picked as the match because it has the most consensus pointsand inliers. This stage involves all or a percentage of all scenefeatures 204 at a time.

Given a set of scene features 204, for example, the model database, andan LSH table generated from the model database, the batch RANSACrecognition method is herein described. This includes an initializationstep, which is setting all likelihood to zero. To begin the batch RANSACmethod, there is provided scene features 204 that are derived from ascene object 202, which equals a number of 3-D points or samples fromactual 3-D surfaces. A scene feature 204 can also equal a spin image.

The next step is to go to several locations on the surface of the 3-Dpoints and compute the 3-D surface descriptors. The model features 206are generated and put into a database a priori. Then, there is generatedan LSH table or indexing from the models database, which is used toaccelerate the indexing/searching process. Given the scene features 204,the question becomes what are the similar model features 206 in themodel database?

After the initialization stage, the next step is the scene feature-basedpruning stage for each scene feature 204. This step provides the mostimage based features in the models database. For example, at this time,there are about a 100 scene features 204 per query. For each scenefeature, there are about 10 to 20 candidate model features 206 for apossibility of 1,000 to 2,000 possible matches. The model features notsimilar to the query will be pruned away. At this time, there will beabout 10,000 to 100,000 pose hypotheses of model features possible forthe correct transformation from scene features to model features.

The next step is the doublet-based pruning step, which occurs where apair of scene features 204 (FIG. 2, section (c)) are matched with a pairof model features 206. The distance and angles are tested. This narrowsdown the amount of surviving pose hypotheses to between about 100 and1,000. For each 100 to 1,000 pose hypotheses, they are warped ortransformed. Once transformed, similarity metrics for the two vehiclesare computed. After computing the likelihood or similarity metrics, thefinal step is to pick the pose hypothesis that generates the maximumlikelihood. In this regard, the highest score is taken. This output isthen used to recognize the object under test. The numerical datadiscussed above is only exemplary to illustrate the present inventionand is not intended to limit the scope of the present invention in anyway.

Alternatively, in addition to using pose transformation information, thepose hypothesis can also be based on a model ID itself. Each modelfeature is in the database, including a hash model ID, for example.

FIG. 3, illustrates a block diagram of a 3-D object recognition deviceor system 300 of the present invention. In one embodiment, the 3-Dobject recognition device or system 300 is implemented using a generalpurpose computer or any other hardware equivalents. All or variouscomponents of system 300 can be adapted to a digital video camera ordigital still camera.

Thus, 3-D object recognition device or system 300 comprises a processor(CPU) 302, a memory 304, e.g., random access memory (RAM) and/or readonly memory (ROM), a 3-D object recognition module 305, and variousinput/output devices 306, (e.g., storage devices, including but notlimited to, a tape drive, a floppy drive, a hard disk drive or a compactdisk drive, a receiver, a transmitter, a speaker, a display, an imagecapturing sensor, e.g., those used in a digital still camera or digitalvideo camera, a clock, an output port, a user input device (such as akeyboard, a keypad, a mouse, and the like, or a microphone for capturingspeech commands).

It should be understood that the 3-D object recognition engine 305 canbe implemented as physical devices that are coupled to the CPU 302through a communication channel. Alternatively, the 3-D objectrecognition engine 305 can be represented by one or more softwareapplications (or even a combination of software and hardware, e.g.,using application specific integrated circuits (ASIC)), where thesoftware is loaded from a storage medium, (e.g., a magnetic or opticaldrive or diskette) and operated by the CPU in the memory 304 of thecomputer. As such, the 3-D object recognition engine 305 (includingassociated data structures) of the present invention can be stored on acomputer readable medium, e.g., RAM memory, magnetic or optical drive ordiskette, and the like.

The processor 302 of the 3-D object recognition device 300 may comprisean image processor. The image processor may receive input from a scenefeatures outside source. The image processor generally comprisescircuitry for capturing, digitizing and processing scene features fromthe outside source. The image processor may be a single-chip videoprocessor and the like.

The processed scene features are communicated to the processor 302. Theprocessor 302 may comprise any one of a number presently available highspeed micro controllers or micro processors. The processor 302 supportedby support circuits 306. The memory 304 also communicates with theprocessor 302. The memory 304 stores certain software routines executedby the processor 302 and by the image processor to facilitate theoperation of embodiments of the present invention, e.g., the variousmethods as discussed above.

The memory 304 also stores data in a database of information used by theembodiments of the present invention, and image processing software usedto process the scene features. Although embodiments of the presentinvention are described in the context of a series of method steps, themethods may be performed in hardware, software, firmware, or somecombination of hardware and software. In a relation to the methodsdescribed above, regarding the recognition of 3-D objects, the device300 may include in the database the models database and the LSH tableand indexing. The image processor also includes the RANSAC method andall pruning methods in the image processing software.

1. A method for recognizing an object, comprising: providing a set ofscene features from a scene; pruning a set of model features; generatinga set of hypotheses associated with said pruned set of model featuresfor said set of scene features; pruning said set of hypotheses; andverifying said set of pruned hypotheses.
 2. The method of claim 1,wherein at least one of said set of hypotheses is used to transform saidscene features into said pruned model features.
 3. The method of claim1, wherein said step of pruning a set of model features comprisesapplying surface descriptor parameters to prune bogus model features. 4.The method of claim 3, wherein said applying step comprises applyinglocality sensitive hashing (LSH) to prune said bogus model features. 5.The method of claim 1, wherein said step of pruning said set ofhypotheses comprises applying doublet-based hypotheses parameters toremove bogus hypotheses.
 6. The method of claim 5, wherein said step ofapplying doublet-based hypotheses parameters comprises: obtaining a pairof scene features for transforming to a corresponding pair of modelfeatures; and generating a pose hypothesis.
 7. The method of claim 6,wherein said step of applying doublet-based hypotheses parameterscomprises associating angle and distance between each sets of pairs. 8.The method of claim 1, wherein said step of verifying said set of prunedhypotheses comprises determining a likelihood of at least onehypothesis.
 9. The method of claim 8, wherein said step of determiningsaid likelihood of at least one hypothesis comprises applying aRANSAC-based verification method.
 10. The method of claim 9, whereinsaid RANSAC-based verification method is a multi-model RANSAC-basedverification method.
 11. A computer-readable medium having storedthereon a plurality of instructions, which, when executed by aprocessor, cause the processor to perform the steps of a method forrecognizing 3-D objects, comprising: providing a set of scene featuresfrom a scene; pruning a set of model features; generating a set ofhypotheses associated with said pruned set of model features for saidset of scene features; pruning said set of hypotheses; and verifyingsaid set of pruned hypotheses.
 12. The computer-readable medium of claim11, wherein at least one of said set of hypotheses is used to transformsaid scene features into said pruned model features.
 13. Thecomputer-readable medium of claim 11, wherein said step of pruning a setof model features comprises applying surface descriptor parameters toprune bogus model features.
 14. The computer-readable medium of claim13, wherein said applying step comprises applying locality sensitivehashing (LSH) to prune said bogus model features.
 15. Thecomputer-readable medium of claim 11, wherein said step of pruning saidset of hypotheses comprises applying doublet-based hypotheses parametersto remove bogus hypotheses.
 16. The computer-readable medium of claim15, wherein said step of applying doublet-based hypotheses parameterscomprises: obtaining a pair of scene features for transforming to acorresponding pair of model features; and generating a pose hypothesis.17. The computer-based medium of claim 16, wherein said step of applyingdoublet-based hypotheses parameters comprises associating angle anddistance between each sets of pairs.
 18. The computer-based medium ofclaim 11, wherein said step of verifying said set of pruned hypothesescomprises determining a likelihood of at least one hypothesis.
 19. Thecomputer readable method of claim 18, wherein said step of determiningsaid likelihood of at least one hypothesis comprises applying aRANSAC-based verification method.
 20. An apparatus for recognizing anobject, comprising: means for providing a set of scene features from ascene; means for pruning a set of model features; means for generating aset of hypotheses associated with said pruned set of model features forsaid set of scene features; means for pruning said set of hypotheses;and means for verifying said set of pruned hypotheses.